ABSTRACT
Two experiments were conducted at the piggery unit of the Department of Animal Science Farm, University of Nigeria, Nsukka, from July 2007 to March 2009, to determine the effect of nutrition and body condition at first mating on the reproductive performance of gilts. The first experiment evaluated the effects of feeding different combinations of protein and energy diets on age at onset of first observed oestrus, growth rate, backfat reserve and body condition score of the gilts from weaning to puberty. Fifty-four (54), eight week old weaner gilts were used for this trial. They were randomly assigned to nine experimental treatment diets having different combinations of protein (16%, 18% and 20% crude protein) and energy (2800 kcal/kg, 3000kcal/kg and 3200kcal/kg) with six (6) gilts per treatment. The gilts in each treatment were housed in pairs making up three (3) replicates per treatment. Estrus detection was carried out twice daily at 0800hr and 1600hrs in the presence of mature boar beginning from the age of five months. Blood samples were collected from two pigs per treatment by humane puncture of the ear vein for haematological and biochemical analysis. In addition, two (2) gilts from each treatment were randomly selected, slaughtered and their reproductive organs excised and examined. Linear body measurements (body length, chest girth, height at withers and flank-to-flank) were also recorded. Data collected were analyzed according to factorial arrangement of treatments in a completely randomized design (CRD) whereas stepwise multiple linear regression analysis was used to generate prediction equations between body weight and linear body measurements. In experiment 2, eighteen (18) gilts with different body conditions and backfat thickness were selected and assigned to experimental treatments with six gilts per treatment. All the gilts were weighed and mated twice at the second observed estrus. Pregnancy was confirmed by the gilt not returning to heat after 21 days of observation for signs of heat after breeding. Gilts were fed 2.1 kg of an 18% CP diet daily throughout gestation. Their feed was increased to 3.0 kg of feed daily during lactation until weaning. Gilts were monitored and their reproductive indices recorded throughout gestation and lactation. The pre-weaning performances of their piglets were also recorded until weaning at day 35. Data collected were subjected to one way analysis of variance (ANOVA) for a completely randomized design (CRD). Results of the first experiment indicated that diet containing 3000kcal/kg or 3200kcal/kg metabolizable energy and 18% crude protein was the optimum required for gilts to grow faster and reach the minimum threshold of age, body weight, backfat reserve and body condition necessary for early attainment of first oestrus and future reproductive processes. On the other hand, the result also showed that when pork of a moderate fatness (lean pork) is in demand, gilts should be fed diets having 2800kcal/kg of metabolisable energy and either 16 or 18% crude protein. High coefficient of determination (R2) values of 0.96, 0.95, 0.93 and 0.45, respectively, were recorded between body (Y) weight and body length (BL), heart girth (HG), flank-to-flank (FF) and height-at-withers (HW) measurements. Prediction equations for body weight of the gilts were, Y = 0.83 x BL – 33.53, Y = 1.07 x HG – 37.86, Y = 1.22 x FF – 37.14 and Y = 0.86 x HW – 14.83. Results of the multiple linear regression showed that with effective management, farmers, researchers and prospective pig buyers can use the prediction equations for body length, heart girth and flank-to-flank measurements to easily estimate the body weight of their pigs especially, during selection, drug administration and/or determination of market weight and prices. In the second experiment, results showed that body condition of gilts at mating affected their gestation weight gain, lactation body weight losses, litter size at birth and weaning, growth rate of their piglets, pre-weaning mortality and weaning-to-estrus intervals, etc in favour of gilts with normal and fat body conditions. It was concluded that in any commercial pig industry where the management is interested in increasing sow lifetime productivity, replacement gilts should be scored for body condition both subjectively and objectively using ultrasonic equipment to determine their readiness to undergo the stress of growth and reproduction. From an economic point of view, this is an important factor that should be considered to determine the total value of pigs produced within a given cycle. Hence, it is recommended that breeding gilts should have at least between 15mm and 18mm backfat thickness at first mating for effective and more balanced reproductive processes.
CHAPTER ONE
1.1 Introduction
Recent report (Spore, 2007) showed that pork is the world most widely consumed meat making up about 40 per cent of the total meat consumed worldwide. The high pork consumption has been attributed to the high cost of beef and the fear of avian influenza for poultry (Spore, 2007). In Africa, however, it barely accounts for 10% of meat consumed. From 1990 to 2005, its production has risen from 500,000 to 800,600 tonnes, probably as a result of rapid urbanization which interestingly has boosted production (Spore, 2007). In Nigeria, FAO (2005) reported a 4 per cent increase in the annual growth rate for pig production from 1990 to 2000 and this was adjudged to be the highest among other livestock species.
These reports are an indication that swine production has the potential for bridging the protein deficiency gap in this country. This is because pigs are endowed with natural genetic potentials that support rapid growth and high reproductive performance. For instance, pigs have a rapid growth rate and demonstrate excellent capacity for reproduction being litter-bearing in nature (Holness, 2005). They are characterized also by the best efficiency of nutrient transformation into high quality animal protein (Spore, 2007). These attributes have not been completely harnessed in this country thus leading to the slow increase in the supply of pork.
The performance of the breeding herd is fundamental to the financial success of any pig enterprise. According to White (1996) and Whittemore (1998), pig production is often assessed based on the number of litters produced per sow per year, the number of piglets produced per litter, and the viability of those piglets. Also, the lifetime productivity of the female within the herd is taken into account. Thus, the young gilt represents the future of any pig enterprise and if not fed properly, is unlikely to achieve her reproductive potential of rearing 60 to 70 pigs over 6 to 7 parities (Scharlach, 1998). It is therefore necessary to provide gilts with adequate nutrition in order to maximize litter growth rate, and minimize empty sow-days thus increasing the size of subsequent litters. Good nutritional preparation of the gilt from selection to first farrowing is essential in achieving this goal. Soede et al. (2007) reported that good nutritional management of gilts makes them to be mature, well grown and in good body condition at service, resulting in better conception rate and litter numbers. They emphasized that far too many gilts are weaned in poor condition and do not conceive or have poor second litters leading to an inexcusable waste of breeding potential.
The types of feedstuff, environment, feeding system for pigs differ around the world, and the nature of these differences is reflected in the growth and reproductive efficiency of pigs around the world. Thus, there is variation within and between temperate and tropical breeds of pigs in age of puberty, maturity, gestation length, age and weight of pigs at weaning which are major determinants of performance (Dritz, 2004; Pluske, 2006). As a result, most pigs in the tropics hardly reach the live weight of those exposed to temperate feeding system. Therefore, it is necessary to categorize pigs in the tropics according to weight ranges obtainable in the zone.
Research reports indicate that nutrition during the rearing of the gilt may influence the length of her reproductive life (Scharlach, 2000; Close, 2003). Scharlach (2000) reported that feeding programs for gilts should be aimed at the female possessing targeted amounts of body fat, bone, and lean at critical points in time such as selection, first breeding or conception, gestation, farrowing, and at weaning. The author noted that maximum longevity is obtained by incorporating the best combination of nutritional regimes during the periods preceding each one of these events (Scharlach, 2000). Therefore, an accurate estimate of fat reserve using both subjective and objective body condition score (BCS) techniques several times during rearing provides targets at which nutritional program can be aimed (Close, 2003).
In modern pig production, nutrition and management play an important role in enhancing reproductive performance of the sow. According to Close (2003), there is need to ensure that the correct target body condition at first mating is achieved and that nutritional needs are met during gestation and lactation. The overall objective is to ensure that, as far as is possible, the sows achieve a good level of performance on all farms.
Condition scoring of pigs allows farmers to determine if their pigs are thriving in the system of management they are kept. Condition scoring is necessary in every type of pig production system as an important management practice. This also applies to other farm animals like sheep, goat, and cattle (Cobb, 2005; Singh-Knights and Knights, 2005; Taiwo et al., 2005). Body condition scoring (BCS) is an estimate of the muscle and fat development of an animal. It can be assigned to an animal either by visual appraisal, by palpation or by combining sight and touch. Animals are given a score from 1 (Emaciated) to 5 (Obese) based on the level of muscling and fat deposition around the loin. It is expected that healthy, well nourished animals should not be too fat or thin.
The body condition of the gilt at first mating has a significant effect on sow lifetime performance. Available records (Gueblez et al., 1985; Gaughan et al., 1995; Challinor et al., 1996) have suggested that animals that do not have sufficient body condition when first....
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